oak.oakland.edu, the
biggest of them all. Check out the cpm, cpmug and sigm directories.
The unix-c/cpm directory contains some portable tools to handle
CP/M files. Alas! This site appears to have gone
off-line owing to a disc crash.

ftp.mayn.de contains a
mirror of most of what was at oakland, in its "archive"
directory. The other directories mirror the CP/M source
archives.

www.retroarchive.org
contains some commercial CP/M software (some of which might be
described as "abandonware"), and a copy of the Walnut Creek CP/M
CDROM. The files from oak.oakland.edu which aren't at ftp.mayn.de
can be found on the
CDROM.